There are plenty of people who are happy about Burger King’s confirmation yesterday that it is in advanced talks to acquire the Tim Hortons coffee shop chain: shareholders, investment bankers, tax lawyers, Timbits fans.

But the execs at the Dunkin’ Brands mother ship in Canton might not be joining in the celebration.

Dunkin’ Brands, under the leadership of CEO Nigel Travis, has made impressive headway, expanding across the country toward the West Coast with a sense of manifest destiny. But that expansion plan — exemplified by the net growth of 371 Dunkin’ shops in the U.S. in 2013 alone — could be threatened if Tim Hortons gets access to a bigger franchise network and Burger King gets a savvier approach to breakfast.

The competition in the breakfast space from the likes of McDonald’s and Taco Bell has already taken a bite out of Dunkin’ Brands. Travis warned investors during a conference call last month that the competition, combined with economic challenges and a rainy spring, caused Dunkin’ to pare back its store revenue projections for the year. But store growth remains on track for now, with another 380 to 410 net new Dunkin’ restaurants expected for the U.S. More than 7,800 Dunkin’ Donuts shops are open in the U.S. today.

Dunkin’ has beat back Tim Hortons before: The company, when it was affiliated with Wendy’s, had expanded into southern New England about a decade ago by taking over what remained of the Bess Eaton doughnut empire. Those shops are gone now, with no Tim Hortons shops remaining in Massachusetts, Connecticut or Rhode Island. But Tim Hortons was able to muscle its way into New York City five years ago, taking over a dozen former Dunkin’ locations in that market.

There will be more street fights like that one, to be sure. Tim Hortons added 55 stores in the U.S. last year, and another seven in the first six months of this year, wrapping up the second quarter with 866 U.S. locations. That kind of pace isn’t enough to threaten Dunks right now. But Darren Tristano, executive vice president at Chicago restaurant consultancy Technomic, tells me the Burger King acquisition could help expedite Tim Hortons’ U.S. expansion plans.

“This will probably accelerate and provide some leverage and strength for Tim Hortons to continue to expand, not just in the Midwest and the East, but also the West Coast,” Tristano says. “Burger King is not going to make Tim Hortons a better brand. But they will use economies of scale.”

The folks at Dunkin' Brands' HQ are playing down the prospects that this acquisition could be a threat to their growth plans. Instead, they say they see this as an opportunity.

"It takes a great deal of time to recognize the potential synergies of mergers like this and it is often distracting for the companies involved," Karen Raskopf, the company's chief communications officer, told me when I inquired about the company's reaction to the BK-Tim Hortons deal. "So we believe this potential merger could give Dunkin' the opportunity to further leverage our many advantages, including our strong relationships with our franchisees, our great store economics and our many growth opportunities including in California where we are opening our newest restaurants months ahead of our 2015 goal."

Tristano concedes that Tim Hortons’ growth did suffer during its tenure under the Wendy’s ownership, but that was mainly because the management focused on the Wendy’s chain. However, with this BK-Tim Hortons merger, the headquarters would move to Tim Horton's home turf in Canada, in part for tax reasons and in part to placate Canadian government officials.

But Tim Hortons could easily pitch its concept to a vast new network of potential franchisees who are already part of the Burger King system, and Tristano says the extra capital could help expedite Tim Hortons’ growth spurt. The deal would make Burger King the third largest fast-food company in the world, after McDonald’s and Yum Brands, with 18,000-plus restaurants and $22 billion in annual system sales. “Overall, this looks great on paper,” Tristano says of the BK play for Tim Hortons, “if it frees up capital and resources and cash flow (for) growth in both brands.”